CN101457521B - An electroosmotic method and equipment for dehydrating large-area high-water-content soil - Google Patents

Abstract

The invention relates to an electroosmotic method used for dewatering the soil with large area and high water content and equipment thereof. The operation comprises the following steps of: (1) constant current starting: adopting a constant current output mode, namely the output current is constant and the output voltage is variable; (2) constant voltage holding: when the output voltage reaches a preset value, the output voltage is converted into stable voltage and then output, namely the output voltage is constant and the output current is variable, and the stable working condition is held for long time; (3) strengthening impulse: in the process of holding constant voltage, impulse voltage is superimposed by a certain interval; (4) energization at intervals: energization and power off are carried out alternatively; and (5) polarity convention: according to the change of water yield, the positive polarity and the negative polarity of output voltage of the special electroosmotic device are automatically changed. By improving the operation method to electroosmotic dewatering, the invention solves the defects in the prior art, improves dewatering efficiency and reduces the energy consumption.

Description

An electroosmotic method and equipment for dehydrating large-area high-water-content soil

technical field

The invention relates to a method for soil dehydration, in particular to an electroosmotic method for dehydrating large-area high-water-content soil, and is especially suitable for occasions such as tidal flat development with high water content, foundation treatment of buildings and structures, and the like.

Background technique

In the development of tidal flats in coastal areas, excavation of foundation pits of buildings and structures in some high water level areas, etc., the problem of how to dehydrate the soil is faced. These soils (soft clay, backfill soil, soil containing organic matter, etc.) generally have the characteristics of high moisture content, high compressibility, and small permeability coefficient. When the treatment area is large, filling and replacement methods should be used for such soil The method is obviously impractical, and only non-filling preloading, compaction, tamping and other methods can be used, and these methods need to be carried out in conjunction with soil dehydration. If the dehydration effect is not good, it will be manifested as low bearing strength and consolidation. The slow speed will seriously affect the construction quality of the upper bearing, so the dehydration effect becomes the key to the effect of soil treatment. Due to the capillary action of the tiny pores of this type of soil, water is kept in the pores, and the permeability is low. The general vacuum dehydration method is not effective, and the electroosmosis dehydration is currently one of the most effective methods.

Electroosmotic dehydration requires electrodes to be arranged in the soil, which are divided into anode and cathode, and a drainage channel is provided near the cathode. When the electrode is fed with direct current, under the action of the electric field, the water in the pores of the soil is combined with the cations, and the water molecules are brought to the cathode, so that the water can be pumped at the cathode, so as to achieve the purpose of discharging the water in the soil.

At present, the actual application of electroosmosis technology in soil dehydration is not common at home and abroad. In some of the few applications, the constant voltage and fixed polarity DC electroosmosis dehydration method is used. This method mainly has the following problems : ①The implementation of constant voltage electroosmosis is simple and feasible, but with the progress of electroosmosis dehydration, the moisture content of the soil decreases, but when it has not yet reached the design requirements, the dehydration efficiency drops significantly, and even the water flow rate with electroosmosis is different from that without The effect of electroosmosis is the same, and the effect of electroosmosis completely disappears. ② For electroosmotic dehydration with fixed polarity, as the electroosmotic dehydration process proceeds, the gas generated by the electrode reaction will accumulate between the soil and the anode, increasing the contact resistance between the two, and correspondingly increasing the voltage drop. The effective electric field strength of the soil weakens, and the dehydration efficiency gradually decreases. Due to the existence of the above situation, the electroosmotic dehydration time is too long, the dehydration energy consumption is high, and the dehydration effect becomes poor. ③ Since the anode will be electrolyzed during the electroosmotic dehydration process, the electroosmotic dehydration method with fixed polarity designs the diameter of the anode to be larger than that of the cathode to prevent the anode from being completely electrolyzed during the electroosmotic dehydration process, causing the electroosmosis to be interrupted. ④ Since the water molecules always gather towards the cathode during the electroosmosis process, and the soil particles are subjected to the force towards the anode, the electroosmotic dehydration with fixed polarity will make the dehydrated soil density and moisture content uneven. ⑤Due to the electrolysis of the anode during the electroosmotic process, the generated oxyhydroxides fill the soil near the anode and play the role of cementing and strengthening the soil, but this phenomenon does not occur at the cathode. It also leads to uneven density of soil after dehydration. All these will affect the bearing strength of the soil.

The existence of the above shortcomings has limited the expansion and application of electroosmotic dehydration technology in engineering.

Contents of the invention

The object of the present invention is to provide an electroosmotic method for dehydrating soil with high water content in a large area, which solves the defects in the existing electroosmotic dehydration technology, improves dehydration efficiency and reduces dehydration energy consumption.

In order to achieve the above object, the technical solution adopted in the present invention is: an electroosmotic method for dehydrating large-area high water content soil, using a special electroosmosis device combined with vacuum pumping to dehydrate the soil, and a special electroosmosis device The operation steps are as follows:

(1) Constant current start: set the initial current and target voltage according to the conductivity of the soil and the depth of electrode embedment, and adopt the steady current output mode, that is, the output current is constant at the initial current, and the output voltage at this time increases with the electroosmotic dehydration. proceed to increase;

(2) Constant voltage maintenance: when the output voltage reaches the set target voltage value, it will switch to a regulated output, that is, the output voltage is constant at the target voltage value;

(3) Pulse strengthening: During the constant voltage holding process, the output voltage is superimposed on the target voltage value with a positive pulse voltage. The amplitude of the pulse voltage is less than or equal to the target voltage value. When there is no pulse, the output voltage is the target voltage value. 20 minutes, the duty cycle is 40% to 60%, and the time for constant voltage maintenance and pulse strengthening is 15 to 24 hours;

(4) Intermittent power-on: power-on and power-off are carried out alternately, each time the power is cut off after 15 to 24 hours of constant voltage maintenance and pulse strengthening, and the power-off time is less than 20 hours. , to discharge the charge, the vacuum pumping at this time continues to be maintained, and steps (2) to (3) are repeated after the power off;

(5) Polarity conversion: When the water output drops to 20-60% of the water output at the beginning of electroosmosis, the polarity of the output voltage changes, that is, the original negative pole becomes positive, and the positive pole becomes negative. Correspondingly, vacuum pumping The position is also switched, and steps (2) to (4) are repeated; when the water output drops to 20% to 60% of the water output at the beginning of the last polarity conversion, the polarity of the output voltage is changed again, and steps (2) are repeated. )～(4), until the moisture content of the soil reaches the predetermined value.

In the above technical solution, the setting method of the initial current is to set the initial current on each electrode according to the conductivity of the soil and the depth of electrode embedment, and set the current linear density of each electrode to 0.1-0.3 amperes/ m, to ensure that the initial current on each electrode does not exceed 1.5 amperes, half of the total number of electrodes multiplied by the initial current value on each electrode is the total output current of the electroosmotic power supply.

The target voltage value is 25 to 30 volts.

In the above technical solution, in the step (1), since the initial moisture content of the soil is high, the electrical conductivity is also high, and due to the limitation of the output current of the electroosmotic device, the output voltage needs to be reduced, so the steady current output mode is adopted. That is, the output current is constant and the output voltage varies. According to the initial current setting of 1.5 amperes on each electrode (adjusted according to the different depth of electrode embedment), as the electroosmotic dehydration proceeds, the conductivity of the soil gradually decreases, and the output voltage gradually increases, making the soil The intensity of the electroosmotic electric field increases correspondingly, the dehydration speed is accelerated, and the dehydration efficiency is improved.

In the step (3), in the process of maintaining the constant voltage, superimpose the pulse voltage at a certain interval (generally 10 minutes), the pulse amplitude is less than or equal to the target voltage value, and the pulse width is about 5 minutes, which is equivalent to 50% of the Duty cycle, the pulse frequency is about 0.5 mHz.

In the step (4), the power-on and power-off are carried out alternately. If one day is a cycle, the power can be turned on for 16 hours and the power is cut off for 8 hours. When the power is turned off, the special electroosmosis device automatically realizes the short circuit between the positive and negative electrodes inside, which is beneficial to The charge is discharged, but the vacuum pumping continues.

In the step (5), the polarity of the electroosmotic power supply is automatically changed according to the change of the water output, that is, when the water output drops to about 30% of the maximum water output, the polarity of the output voltage is changed, and the original negative pole becomes positive. The positive pole becomes the negative pole, and accordingly, the position of vacuum pumping is also switched.

Due to the use of the above-mentioned technical solutions, the present invention has the following advantages compared with the prior art:

1. By improving the electro-osmosis dehydration operation method, the present invention solves the defects existing in the electro-osmosis dehydration operation in the past, greatly improves the dehydration efficiency, reduces energy consumption, and is more suitable for popularization and use.

2. Superimpose the pulse voltage, under the condition that the effective value of the electroosmotic voltage remains unchanged, the peak output voltage will be increased for a short time, and the kinetic energy of the water molecules will be increased, so that the capillary of the soil can be opened more effectively and the soil can be increased. The permeability coefficient can improve the efficiency of electroosmotic dehydration.

3. During the process of electroosmosis, a charge accumulation effect is generated in the soil. Excessive accumulated charges prevent the movement of weakly bound water. During the power-off period of intermittent energization, because the electrodes are short-circuited, the accumulated charges can be released as soon as possible, which improves the electroosmosis. Dehydration effect is also beneficial to save electricity.

4. The polarity conversion makes the gas formed near the original positive electrode (the negative electrode after the polarity change) change from gas phase to liquid phase with the accumulation of water, thereby reducing the contact resistance and increasing the effective electric field strength of the soil. Further improve the dehydration efficiency. On the other hand, the geometric dimensions of the cathode and anode electrodes can be made the same, and both can be used once. After the electroosmotic dehydration is completed, there are electrolytic hydroxide compounds filling the soil near the two electrodes, both of which play a role in cementing and strengthening the soil, so that the density and moisture content of the soil after electroosmotic dehydration are kept basically uniform.

Description of drawings

Fig. 1 is a schematic diagram of the electroosmotic operation process of an embodiment of the present invention;

Fig. 2 is a schematic block diagram of the electroosmosis device in the embodiment of the present invention.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Embodiment one

As shown in Figure 1, an electroosmotic method for dehydrating large-area high-water-content soil, its operation steps are as follows:

1. Positioning, burying electrodes, inserting drainage boards

Accurately position according to the layout requirements and then bury the electrodes and insert the drainage board. The height above the ground is 0.1m, and the coarse sand is poured. The negative and positive electrodes are arranged in parallel and staggered. The corresponding electrode of the infiltration device; in order to prevent the current from excessive diversion from the soil surface, reduce the effect of electroosmosis and the occurrence of electric corrosion effect, the exposed metal parts above the ground of the cathode and anode should be cleaned before energization, and a layer of asphalt should be applied to reduce the electric current. Consumption; the two ends of the connection between the drain board and the main pipe are tightened with tight hoops to prevent air leakage.

2. Geotextile and membrane covering

The PVC composite geomembrane is laid, and the sealing film is assembled into a whole piece of plastic film larger than the treatment area in the dehydration area. After laying the first layer of plastic film, you should check whether there is any air leakage at the joints and repair it in time. During the film laying process, use soil bags to press the film to prevent the wind from blowing away or tearing the laid film. The construction personnel work or walk on the membrane with hard-soled shoes to prevent the membrane from being scratched. When the membrane is laid, a small number of vacuum pumps are installed to work to suck the laid membrane.

3. Vacuum pumping and preloading

The vacuum pump pumps air, so that there is a pressure difference between the inside and outside of the membrane, and this pressure difference is the load acting on the soil. As the air in the membrane is continuously discharged, the air pressure difference gradually increases, and the water and air in the soil are continuously discharged to cause the foundation to consolidate. After the water output of vacuum pumping and pre-pressing is significantly reduced (usually indicating that the water flow rate is reduced to below 20% of the initial flow rate), the power supply is turned on for electroosmotic dehydration.

4. Electroosmotic operation

Turn on the power supply of the electroosmotic power supply device, set the initial current, hold voltage, hold time, pulse strengthening time, power-on time, intermittent time, water volume ratio for polarity conversion (such as 30%) and other parameters, and connect the water flow acquisition signal.

The entire power supply device can be operated automatically, and the operation process is shown in Figure 2:

(1) Constant current start: 4 electrodes are embedded in the soil to a depth of 2 meters, the current of each electrode is set to 0.6 amperes, the initial current is 1.2 amperes and the target voltage value is 27 volts, and the steady current output mode is adopted, that is, the output current The initial current is constant at 1.2 amperes, and the output voltage increases with the electroosmotic dehydration at this time;

(2) Constant voltage maintenance: When the output voltage reaches the set target voltage value of 27 volts, it will switch to a regulated output, that is, the output voltage is constant at the target voltage value;

(3) Pulse strengthening: During the constant voltage holding process, the output voltage is superimposed on the target voltage value with a positive pulse voltage. The pulse voltage is 25 volts. When there is no pulse, the output voltage is the target voltage value. The cycle is 10 minutes, and the duty cycle 40%, the time for constant pressure maintenance and pulse strengthening is 15 hours;

(4) Intermittent power-on: power-on and power-off alternately, each time after 15 hours of constant voltage maintenance and pulse strengthening power-on, power-off time is 10 hours, when power-off, the output positive and negative poles are short-circuited to prevent leakage. Discharge the charge, continue to maintain the vacuum pumping at this time, and repeat steps (2) to (3) after the power off;

(5) Polarity conversion: When the water output drops to 30% of the water output at the beginning of electroosmosis, the polarity of the output voltage changes, that is, the original negative pole becomes positive pole, and the positive pole becomes negative pole. Correspondingly, the vacuum pumping position also changes. Switch and repeat steps (2) to (4); when the water output drops to 30% of the water output at the beginning of the last polarity switch, the polarity of the output voltage is changed again, and repeat steps (2) to (4 ), until the moisture content of the soil reaches a predetermined value.

Start the electroosmotic power supply equipment, observe whether the output current and voltage are normal, and make necessary adjustments if necessary.

After the equipment is in normal operation, arrange personnel to be on duty 24 hours a day to eliminate possible failures such as vacuum leakage, mesh blockage, abnormal operation of electromechanical equipment, etc., and keep records on duty.

According to the actual situation, the special electroosmosis equipment can be set to automatic operation state or manual operation state. Embodiment two

The difference from Example 1 is:

(1) Constant current start: 6 electrodes are embedded in the soil at a depth of 5 meters, and the current of each electrode is set to 0.5 amperes, the initial current is 1.5 amperes and the target voltage value is 30 volts, and the steady current output mode is adopted, that is, the output current The initial current is constant at 1.5 amperes, and the output voltage increases with the electroosmotic dehydration at this time;

(2) Constant voltage maintenance: When the output voltage reaches the set target voltage value of 30 volts, it will switch to a regulated output, that is, the output voltage is constant at the target voltage value;

(3) Pulse strengthening: During the constant voltage holding process, the output voltage is superimposed on the target voltage value with a positive pulse voltage. The pulse voltage is 27 volts. When there is no pulse, the output voltage is the target voltage value. The cycle is 15 minutes, and the duty cycle 60%, the time for constant pressure maintenance and pulse strengthening is 20 hours;

(4) Intermittent power-on: power-on and power-off are carried out alternately, each time the power is cut off after 20 hours of constant voltage maintenance and pulse strengthening, and the power-off time is 15 hours. Discharge the charge, continue to maintain the vacuum pumping at this time, and repeat steps (2) to (3) after the power off;

(5) Polarity conversion: When the water output drops to 20% of the water output at the beginning of electroosmosis, the polarity of the output voltage changes, that is, the original negative pole becomes positive, and the positive pole becomes negative. Correspondingly, the vacuum pumping position also changes. Switch and repeat steps (2) to (4); when the water output drops to 20% of the water output at the beginning of the last polarity switch, the polarity of the output voltage is changed again, and repeat steps (2) to (4 ), until the moisture content of the soil reaches a predetermined value.

Other steps are the same as in Embodiment 1.

Embodiment three

The difference from Example 1 is:

(1) Constant current start: 2 electrodes are embedded in the soil to a depth of 5 meters, and the current of each electrode is set to 0.2 amperes, the initial current is 1.0 amperes and the target voltage is 25 volts, and the steady current output method is adopted, that is, the output current The initial current is constant at 1.0 ampere, at this time the output voltage increases with the electroosmotic dehydration;

(2) Constant voltage maintenance: When the output voltage reaches the set target voltage value of 25 volts, it will switch to a regulated output, that is, the output voltage is constant at the target voltage value;

(3) Pulse strengthening: During the constant voltage holding process, the output voltage is superimposed on the target voltage value with a positive pulse voltage. The pulse voltage is 20 volts. When there is no pulse, the output voltage is the target voltage value. The cycle is 20 minutes, and the duty cycle 50%, the time for constant pressure maintenance and pulse strengthening is 24 hours;

(4) Intermittent power-on: power-on and power-off are carried out alternately, each time the power is cut off after 24 hours of constant voltage maintenance and pulse strengthening, and the power-off time is 20 hours. Discharge the charge, continue to maintain the vacuum pumping at this time, and repeat steps (2) to (3) after the power off;

(5) Polarity conversion: When the water output drops to 60% of the water output at the beginning of electroosmosis, the polarity of the output voltage changes, that is, the original negative pole becomes positive pole, and the positive pole becomes negative pole. Correspondingly, the vacuum pumping position also changes. Switch and repeat steps (2) to (4); when the water output drops to 60% of the water output at the beginning of the last polarity switch, the polarity of the output voltage is changed again, and repeat steps (2) to (4 ), until the moisture content of the soil reaches a predetermined value.

Other steps are the same as in Embodiment 1.

Actual experiments were carried out using the method of the present invention.

Experiments show that the intermittent energization and polarity conversion of this technology can reduce the degree of electric corrosion of electrodes compared with constant voltage and fixed polarity direct current electroosmosis, and can save electrode material costs and construction costs by 20%.

This technology was used in the development of tidal flats and excavation of foundation pits. The results show that the dehydration rate is 30% faster than that of vacuum dehydration without electroosmosis, and 15% faster than that of DC electroosmosis with constant voltage and fixed polarity. Soil consolidation is accelerated. The construction period can be shortened by 15%, and the electric energy can be saved by 25%. It solves the problems of poor electroosmotic dehydration efficiency and serious electro-corrosion effect of the anode electrode that cannot be solved by the current fixed voltage and fixed polarity DC power supply electroosmotic dehydration technology, which can not only improve the dehydration efficiency, but also reduce energy consumption.

Claims (3)

1. An electroosmotic method for dehydration of large-area high water content soil, adopting electroosmotic device in conjunction with vacuum pumping to carry out dehydration treatment of soil, is characterized in that: the operation steps of electroosmotic device are as follows: (1) Constant current start: set the initial current and target voltage according to the conductivity of the soil and the depth of electrode embedment, and adopt the steady current output mode, that is, the output current is constant at the initial current, and the output voltage at this time increases with the electroosmotic dehydration. proceed to increase; (2) Constant voltage maintenance: when the output voltage reaches the set target voltage value, it will switch to a regulated output, that is, the output voltage is constant at the target voltage value; (3) Pulse strengthening: During the constant voltage holding process, the output voltage is superimposed on the target voltage value with a positive pulse voltage. The amplitude of the pulse voltage is less than or equal to the target voltage value. When there is no pulse, the output voltage is the target voltage value. 20 minutes, the duty cycle is 40% to 60%, and the time for constant voltage maintenance and pulse strengthening is 15 to 24 hours; (4) Intermittent power-on: power-on and power-off are carried out alternately, each time the power is cut off after 15 to 24 hours of constant voltage maintenance and pulse strengthening, and the power-off time is less than 20 hours. , to discharge the charge, the vacuum pumping at this time continues to be maintained, and steps (2) to (3) are repeated after the power off; (5) Polarity conversion: When the water output drops to 20-60% of the water output at the beginning of electroosmosis, the polarity of the output voltage changes, that is, the original negative pole becomes positive, and the positive pole becomes negative. Correspondingly, vacuum pumping The position is also switched, and steps (2) to (4) are repeated; when the water output drops to 20% to 60% of the water output at the beginning of the last polarity conversion, the polarity of the output voltage is changed again, and steps (2) are repeated. )～(4), until the moisture content of the soil reaches the predetermined value. 2. The electroosmosis method according to claim 1, characterized in that: the setting method of the initial current is to set the initial current on each electrode according to the conductivity of the soil body and the depth of electrode embedment, and set the initial current for each electrode. The current linear density of the root electrode is 0.1-0.3 ampere/meter, to ensure that the initial current on each electrode does not exceed 1.5 ampere, half of the total number of electrodes multiplied by the initial current value on each electrode is the total output current of the electroosmosis power supply . 3. The electroosmotic method according to claim 1, wherein the target voltage is 25 to 30 volts.

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